Known oscilloscopes comprise a trigger unit which is needed in order to obtain a static image of a measured signal. In normal mode, the trigger unit halts a renewal of the image until a certain trigger condition is satisfied, for example an input voltage level (trigger level) and a direction in which the input voltage level is crossed.
In automatic mode, the trigger unit initiates a renewal of the image after a predefined time called auto-trigger time even if the trigger condition has not been met.
If a frequency of the input signal is low, and more precisely, if the frequency is such that a time between two parts of the measured signal meeting the trigger condition exceeds the auto-trigger time, the image of the measured signal becomes unstable. This is due to the image being renewed alternately because of the trigger condition met and the auto-trigger time exceeded, respectively.
In known oscilloscopes, a static image of such a measured signal of low frequency can be obtained by switching to normal mode. However, the image will only be renewed when the trigger condition is met because the auto-trigger is switched off.
Accordingly, there is a need for an oscilloscope acquisition system as well as a method for operating an oscilloscope acquisition system that is capable of obtaining a static image of a measured signal of low frequency while retaining an operative auto-trigger.